THE SHAP GRANITE AXD ASSOCIATED ROCKS. ti07 



crossed nicols a distinct crvstalliue reaction, polarizing in low tints 

 like those of quartz. The brown colouring-matter is too minutely 

 divided and too densely collected to admit of determination, but it 

 is probably to be referred to mica. A similar substance is found 

 ill the metamorphosed fine pyritous ashes north of Blea Beck Bridge, 

 and here it is certainly brown mica, the flakes being large enough 

 for the pleochroism and other characters to become evident [8(59], 

 Here too, at (350 to 700 yards from the granite, the light spots are 

 larger (up to about y^^ inch in diameter), but only the smallest of 

 them behave in polarized light as single crystals. It may be re- 

 marked in passing that the andesite fragments in the breccias show 

 the same development of brown mica as the matrix [1072, 11 66 J. 



There can be no doubt that the brown mica in these rocks is of meta- 

 morphic origin. It is absent in all specimens taken at places remote 

 from the granite, and, up to a certain point, becomes more distinctly 

 separated out, and in larger flakes, as we approach the intrusion. 

 In some cases the mica is seen to have been formed especially in the 

 neighbourhood of crystals of magnetite, from which the mineral 

 presumably obtained the iron necessary for its composition. This 

 is seen in some of the rocks which crop out on the moor west of 

 the Hotel, about 1000 yards from the granite-boundarj^ [1076]. 

 Some of the rocks in this neighbourhood, however, show but little 

 modification which can be ascribed to thermal action [1073], making 

 it appear that the metamorphism does not depend in a verj^ strict 

 manner upon distance from the intrusion ; but, in view of the 

 faulted character of the ground, it would be unsafe to draw any 

 conclusions from this fact. 



We pass on to consider the more complete metamorphism of 

 rhyolitic ashes seen in exposures nearer to the contact. About 250 

 yards from the eastern margin of the granite some highly altered 

 ashes are exposed in a disused quarry on the old Shap road, and 

 similar rocks crop out at one or two places on the neighbouring 

 moorland. Almost every trace of original constitution is lost, but 

 what remains is sufficient to show that the rocks were felspathic 

 ashes. The lamination is indicated by the arrangement of flakes of 

 brown mica and by streaks rich in opaque iron ores. The mica 

 seems to have been derived from a green chloritoid mineral with 

 low polarization-tints, some of which remains unaltered. The 

 iron ores include ilmenite as well as magnetite, and occur as little 

 crystals and minute granules having the appearance of metamorphic 

 products. A clear colourless mica is sparingly present, and a 

 characteristic mineral is disthene, of the pale blue variety known as 

 cyanite, which is abundant in the slides in little imperfect crystals 

 and clusters of granules. The bulk of the rock, however, consists 

 of a fine-grained crystalline aggregate of felspar. The water-clear 

 crystals mostly show some approach to rectangular contours, the 

 cleavage is often well seen, and twinning is not uncommon ; but we 

 are not able to say with certainty that quartz is not present in sub- 

 ordinate quantity. It is evident, at least, that the bulk is of felspar, 

 and that the whole was formed hi siiit during the metamorphism. 



